Therapeutic Potential of Gut Microbiota and Its Metabolite Short-Chain Fatty Acids in Neonatal Necrotizing Enterocolitis

Short chain fatty acids (SCFAs), the principle end-products produced by the anaerobic gut microbial fermentation of complex carbohydrates (CHO) in the colon perform beneficial roles in metabolic health. Butyrate, acetate and propionate are the main SCFA metabolites, which maintain gut homeostasis and host immune responses, enhance gut barrier integrity and reduce gut inflammation via a range of epigenetic modifications in DNA/histone methylation underlying these effects. The infant gut microbiota composition is characterized by higher abundances of SCFA-producing bacteria. A large number of in vitro/vivo studies have demonstrated the therapeutic implications of SCFA-producing bacteria in infant inflammatory diseases, such as obesity and asthma, but the application of gut microbiota and its metabolite SCFAs to necrotizing enterocolitis (NEC), an acute inflammatory necrosis of the distal small intestine/colon affecting premature newborns, is scarce. Indeed, the beneficial health effects attributed to SCFAs and SCFA-producing bacteria in neonatal NEC are still to be understood. Thus, this literature review aims to summarize the available evidence on the therapeutic potential of gut microbiota and its metabolite SCFAs in neonatal NEC using the PubMed/MEDLINE database.


Introduction
The gut microbiota composition and function undergo drastic changes during the first years of life [1] that are characterized by early microbial colonization with Escherichia and Bifidobacterium, which are gradually decreased following weaning and replaced by species of obligate anaerobic bacteria within the Firmicutes phylum, such as Coprococcus, Enterococcus, Roseburia and Clostridium [2][3][4]. The short-chain fatty acids (SCFAs), butyrate, propionate and acetate, are the main metabolic products of gut microbial Firmicutes phyla fermentation of complex non-digestible dietary substrates, such as fiber and resistant starch [5]. Bifidobacterium and lactic acid bacteria (LAB) produce lactate, which acts as an intermediate fermentation product for butyrate production [6]. In general, Bifidobacterium spp. are considered the primary colonizers of the breastfed infant gut, mainly due to the presence of human milk oligosaccharides (HMOs) [7][8][9][10]. The degradation of HMOs and complex carbohydrates (CHO) could result in high SCFA production (mainly butyrate and acetate), which can be used by other butyrogenic bacteria, such as Faecalibacterium prausnitzi (F. prausnitzi), Bacteroides and Roseburia, for growth by cross-feeding [7,8]. SCFAs produced by the infant-type Bifidobacterium spp. can enhance immunomodulatory responses by reducing inflammatory cytokines through the microbiota-gut-brain axis [10].
Necrotizing enterocolitis (NEC) is a severe inflammatory necrosis of the distal small intestine/colon that primarily affects preterm (less than 32 weeks' gestation) or very low birth weight (VLBW: <1500 g) infants after the introduction of enteral feeds. NEC is characterized by hyperosmolar injury and intestinal ischemia, which reduce the integrity of the epithelial barrier that is evident by peritonitis, hemodynamic instability, abdominal tenderness/cellulitis, acute feeding intolerance, bacteremia and abdominal distension [11,12].
Pregnancy and lactation perform a crucial role in shaping the composition of infant gut microbiota, which is influenced by a range of pre-and post-natal factors, such as antibiotic exposure, lactation stage, gestational age, mode of feeding/delivery, diet and body mass index (BMI) [3,17,21]. Maternal diet during pregnancy and lactation has been linked to an increased risk of developing obesity and asthma in the infant's early years of life [22,23] and the mechanisms underlying such effects are postulated to be the alterations in maternal/infant gut microbiota and/or milk microbiota [21]. A high-fiber diet during pregnancy and lactation increases SCFAs production [21][22][23][24][25][26]. SCFAs are essential for differentiation of helper T cells (Th1, Th2) by their binding to G-protein coupled receptors (GPCRs), including free the fatty acid 2/3 receptor (FFAR2, FFAR3) present in the colon, thereby maintaining gut homeostasis and regulating inflammation by reducing the expression of pro-inflammatory cytokines [24,25]. Higher levels of SCFAs detected in breastmilk may enhance the neonatal anti-inflammatory immune responses by inducing factor fork head box protein 3 (FOXP3 + ) regulatory T (T reg ) cell differentiation in the gut [27]. Breastmilk is a source of secretory IgA immunoglobulin A (SIgA) and IgA-producing antibody-secreting cells (ASCs), which regulate early gut microbiota maturation and immunity by binding to SCFA-producing Bifidobacterium and Lactobacillus, resulting in reduced NEC-related inflammation in preterm infants [28]. It has been suggested that infant feeding with probiotics-supplemented formulas and solid/complementary foods alter gut microbiota composition during the first years of life [9,[29][30][31]. Evidence from randomised controlled trials (RCTs) has shown that NEC-specific treatments, such as oral lactoferrin combined with probiotics and parenteral/oral supplementation with arginine, reduce the disease risk [13,[32][33][34][35]. Probiotic supplementation with Bifidobacterium and Lactobacillus strains, prebiotics (e.g., HMOs), synbiotics (mixtures of probiotics and prebiotics), long chain polyunsaturated fatty acid (PUFA) and bovine colostrum were also demonstrated by a large number of human RCTs, to be effective preventive strategies for NEC, which are thought to modulate the immune response and increase the abundance of beneficial gut microbes [36][37][38][39]. Breastfeeding has been demonstrated to have a protective role against NEC due to its potential to promote the colonization of commensal bacteria and decrease the susceptibility to gut dysbiosis in premature infants [40,41].
SCFAs contribute as mechanisms linking diet, gut microbiota and human health [5], resulting in induced epigenetic changes in the gene patterns of offspring, thereby being a potential epigenetic target in the treatment of gastrointestinal diseases during the first years of life. SCFAs could alter DNA and histone methylation patterns in several genes, resulting in reduced cytokines and chemokines with pro-inflammatory effects in the infant's gut [22,23]. Findings from recent reviews in infants/children have demonstrated the potential efficacy of SCFA-producing bacteria in reducing inflammation-related disease risk, including obesity, asthma and inflammatory bowel diseases (IBD) [22,23,42]. However, no reviews yet discuss the role of SCFAs and SCFA-producing bacteria as therapeutic agents against neonatal NEC. Thus, this review aims to explore the therapeutic role of gut microbiota and its metabolite SCFAs in neonatal NEC. It is hypothesized that gut microbialderived SCFA metabolites can be regarded as having health benefits in neonatal NEC. Preterm infants with NEC who are fed breastmilk/formula and/or supplemented with probiotics/prebiotics are postulated to have higher SCFA levels and abundance of SCFAproducing bacteria, which may perform a significant role in modulating the inflammatory immune responses of immature intestinal cells.

Methods
A literature search of PubMed/MEDLINE database was performed up to December 2022 to identify studies exploring the potential role of gut microbiota and its metabolite SCFAs in NEC treatment using the following keywords "NEC", "preterm/premature infants", "immature intestinal cells", "intestinal inflammation", "inflammatory biomarkers", "gut microbiota", "epigenetic", "SCFAs", "probiotics/prebiotics" and "feeding types". The search was limited to retrieve human studies published in English irrespective of design.

Epigenetics and Inflammatory Biomarkers in NEC
Epigenetic alternation in the immature intestine, such as changes in DNA methylation and long non-coding RNA (lncRNA) patterns, may contribute to increased risk of NEC. Epigenetic changes are attributed to prenatal and postnatal factors (e.g., microbiome, intrauterine infection and enteral feeding) that may affect intestinal function/structure and cause upregulation of pro-inflammatory cytokines [43,44]. DNA methylation changes in cytosine-phosphate-guanine dinucleotides (CpG) regions of NEC-related genes are related to disease risk. For example, high levels of CpG methylation in the DNMT3A, TNT2/3, TNIP1, GALNT6 and HNF4 genes have been identified in stools and colons of premature infants with NEC [45][46][47]. An association of CpG methylation in the cytokine Oncostatin M (OSM) with NEC has also been observed, which can induce intestinal inflammation [47]. The hypermethylation of four genes (MPL, KDM6A, ZNF335 and RASAL3) has been reported in the intestine of neonatal NEC, which is associated with lymphocyte proliferation and intestinal epithelial permeability [48]. Analyses of CpG methylation positions in the intestinal epithelial cells of neonatal NEC revealed a significant hypermethylation in five genes (toll-like receptor 4; TLR4, ENOS, EPO, DEFA5 and VEGFA) at three sites [49]. Overexpression of micro-431 (miR-431) in the intestinal tissues of neonatal NEC results in significantly inhibited FOXA1 and HNF4A and increased pro-inflammatory (e.g., interleukins IL-6, IL-8, IL-10, LGR5, tumor necrosis factor-α; TNF-α and PRKCZ) gene expression in response to lipopolysaccharide (LPS) stimulation [50]. lncRNA influences the expression of mRNAs in the intestine tissues of neonatal NEC by upregulating expression levels of IL-6, IL-1β and TLR4 after LPS exposure, which induces activation of peroxisome proliferator-activated receptors (PPARs) and phosphatidylinositol-3 kinase/serine-threonine kinase (PI3K-AkT) signaling pathways, suggesting that lncRNA contributes to NEC pathogenesis [51].
NEC is characterized by decreased FOXP3 + T reg cell levels and gut expression of transforming growth factor β (TGF-β). Infants with NEC displayed elevated levels of nitric oxide (NO) and high cytokine expression levels with pro-inflammatory effects (e.g., Nuclear factorκ B; NFκ B, tumor necrosis factor-α; TNF-α, interferon; IFN-γ, IL-6, IL-8, IL-10, IL-1β) induced by LPS and produced by the cells of the adaptive immune system in response to colonization by pathogenic bacteria (e.g., Staphylococcus spp., and Clostridium spp.), thereby disturbing the integrity of epithelial tight junctions [52][53][54][55][56][57][58]. An experimental study has shown overexpression of TLR2 and TLR4 receptor-mediated IL-8 mRNA expression in the immature intestine of neonatal NEC [59]. Data from a human NEC experiment showed that pro-inflammatory cytokine expression of IL-1β, IL-1A, IL-6, TNF-α and IL-36 isoforms IL36A were increased in epithelial cells, whereas cytokines IL-37 and IL-22, which are considered protective, were decreased [60]. Evidence from an experimental study showed that IL-17F expression and its related pro-inflammatory C-X-C motif chemokines ligand 8 and 10 (CXCL8, CXCL10) are upregulated in the intestine of neonatal NEC [61]. A case-control study demonstrated higher levels of TNF-α, IL-8, IL-1β and lower levels of TGF-β, FOXP3 + T reg and IL-10 in the ileum of surgical NEC patients compared with matched controls (patients with spontaneous intestinal perforation/congenital intestinal atresia) [18]. Another case-control study showed that the levels of serum TNF-α, IL-6 and intestinal fatty acid-binding protein (I-FABP) were higher in NEC patients than non-NEC counterparts [62]. In a recent experimental study, preterm newborns displayed increased mRNA expression of fecal cytokines IL-1α/β, IL-7 and IL-12p40 [20]. This suggests that preterm infants with NEC display intestinal inflammation with markedly increased pro-inflammatory cytokines and chemokines, in which DNA methylation and lncRNA as epigenetic mechanisms are involved.

Insights into the SCFA-Producing Bacteria in Preterm Infants
SCFAs produced by gut microbiota act as epigenetic mechanisms in reducing intestinal inflammation by inducing DNA/histone methylation changes in the gene patterns of infants [22,23,42]. On this basis, it is important to provide an overview of SCFA-producing bacteria, such as Bifidobacterium, Lactobacillus, Enterococcus and Bacteroides, that may perform a crucial role in protecting from NEC-related inflammation.
The role of SCFAs in neonatal NEC treatment remains controversial. High luminal SCFAs production (e.g., butyric acid) by bacterial colonization in preterm infants is due to poor gastrointestinal motility and carbohydrates malabsorption [63]. Enteric bacterial pathogens, including Clostridium perfringens (C. perfringens), C. difficile, C. paraputrificum, C. butyricum and Klebsiella pneumoniae (K. pneumoniae) have shown to be implicated in NEC via increasing butyric acid production as result of lactose fermentation [64]. A high production of butyric acid by C. butyricum increases inducible nitric oxide synthase (iNOS) gene expression responsible for mucosal injury in NEC [65]. These findings suggest that excessive SCFAs produced by pathogenic bacteria may reduce the intestinal epithelial barrier integrity and increase metabolic inflammation in neonatal NEC. Thus, it is proposed that SCFA-producing commensal microbes (e.g., Bifidobacterium, Lactobacillus) may contribute to the regulation of gut immune homeostasis.
Analysis of the fecal and meconium microbiota of preterm infants revealed a high abundance of Enterococcus [80,89,90]. E. faecalis and E. faecium constitute the most dominant Enterococcus of fecal microbiota in preterm infants [80]. The genus Enterococcus belongs to a large group of LAB in the class Bacilli that is typically identified as facultative anaerobic bacteria within the Firmicutes phylum [66,79,91]. Enterococcus spp. produce L(+)-Lactic acid as the main end metabolic product yielded from sugar fermentation [86]. Enterococcus increases the production of acetate, propionate and butyrate in pre-weaned and weaning infants' feces upon fermentation of resistant starch [78]. The E. faecalis strain ATCC19433 exhibits growth in response to fucosylated HMOs (2 -FL or 3-FL) and produces lactate [92]. The E. faecalis strain AG5 has been found to assimilate cholesterol and produce propionate in vitro [93].
Multiple Streptococcus spp. (S. thermophilus, S. mitis, S. anginosus and S. sanguinis) dominated the meconium microbiome of preterm infants during the first 21 days of early life [80]. The genus Streptococcus is a facultative anaerobe Gram-positive bacteria within the Firmicutes phylum [94]. S. thermophilus has been shown to produce L(+)-Lactic acid as the major fermentative end-product [86]. Such species can use the acetyl-CoA "Wood-Ljungdahl" pathway of carbon dioxide (CO2) fixation as the main mechanism for transforming pyruvate to acetate [95]. Fucosylated HMOs (2-FL or 3-FL) are found to be metabolized into lactate by the S. thermophilus strain ATCC19258 [92].
The genus Bacteroides that belongs to the phylum Bacteroidetes, is the most abundant Gram-negative anaerobic bacteria in the fecal microbiota of preterm infants [96]. B. fragilis was the species that predominated in the fecal microbiota of preterm infants in the first weeks of life [97,98]. Bacteroides spp. have large genomes with extremely high numbers of carbohydrate cleaving enzymes [99][100][101], which degraded complex oligosaccharides, such as mucin glycans [102] and HMOs [103][104][105]. Butyrate, acetate and propionate were the major end-products of resistant starch fermentation generated by Bacteroides spp. in weaned infants' feces [78]. The acetyl-CoA and succinate pathways are the major routes for the production of acetate and propionate, which exist mainly in Bacteroides spp. [95,[106][107][108].

Effects of Feeding Types on Gut Microbiota and Its Metabolite SCFAs in Preterm Infants
Evidence from several prospective cohort studies and RCTs suggests that breastmilk and/or formula with probiotics/prebiotics may have the potential to enhance the growth of SCFA-producing bacteria and increase SCFAs levels in preterm infants.

Prospective Cohort Studies
A cohort study over 1-year period has demonstrated the potential of breastmilk and formula to influence fecal SCFA profiles in LBW preterm infants. The concentrations of fecal acetate and propionate were found to be higher in infants who were fed breastmilk, whereas the concentrations of fecal butyrate were higher in those fed Similac special care formula [109]. It has been has shown that premature infants fed formula have higher concentrations of butyrate and acetate, while those fed breastmilk have higher concentrations of propionate in their feces over 1-year follow-up. This may be due to the colonization of SCFAproducing Bifidobacterium and Lactobacillus influenced by breastmilk and formula [110]. A study evaluated the beneficial effects of probiotics supplementation in preterm infants over 100-day period and found that a combination of B. bifidum with L. acidophilus (Bif/Lacto) increases fecal lactate levels and the abundance of Bifidobacterium spp. consistent with their ability to metablize HMOs into acetate [111].
Over a 10-year longitudinal study, preterm infants who were fed breastmilk or supplemented with two different probiotics (Infloran and Labinic) showed a significant increase in the relative abundance of Bifidobacterium spp. and a significant decrease in the relative abundance of pathogenic bacteria in their feces. The study suggests that long-term colonization of Bifidobacterium depends on the type of probiotics used [112]. In a recent study, with follow-up over 1 year, aimed to identify variation in fecal microbiota from admission to discharge, preterm infants who were fed breastmilk demonstrated a higher abundance of Bifidobacterium spp. and lower abundance of Veillonella. However, infants who were fed probiotic formula demonstrated a lower abundance of Lactobacillus [113]. A cohort study showed that the gut microbiota colonization varied among preterm infants as a result of probiotic formula-feeding. Bifidobacterium and Lactobacillus were found in higher abundance in the fecal microbiota of preterm infants fed with formula supplemented with probiotic B. lactis over 3-month period [114]. Use of the probiotic B. longum subsp. infantis EVC001 in conjunction with breastmilk has been shown to increase the gut microbiome abundance of Bifidobacteriaceae and decrease the abundance of Staphylococcaceae and Enterobacteriaceae associated with gut dysbiosis and antibiotic-resistance in preterm infants in longitudinal 5 months of follow-up [115]. The relative abundances of Bifidobacterium spp.
have been found to increase the fecal microbiota of preterm infants fed with breastmilk and human donor milk during the first three months of life [116]. In a study conducted to examine the effect of breastmilk, donor human milk or formula on shaping the fecal microbiota of preterm infants during the first month of life, infants fed with mother's own milk have higher fecal SCFA-producing bacteria compared with those fed donor human milk or formula [117]. A previous study found that breastmilk influences the microbial colonization of preterm infants over the first 30 days of life. Breastmilk fed infants have higher abundance in Lactobacillus and Granulicatella than non-breast milk fed infants [118].
A study found that oral administration of B. breve M-16V to LBW infants resulted in increased fecal abundance of Bifidobacterium and Enterococcus 10 weeks post-administration. This is attributed to acetic acid, which may inhibit the growth of Proteobacteria, thus providing a suitable environment for SCFA-producing bacteria growth [119]. Evidence from a cohort study supports supplementation with multiple-strain probiotics including bifidobacteria in preterm infants. Three Bifidobacterium strains have been administrated in infants showing lower detection rates of Enterobacteriaceae and higher rates of bifidobacteria in the feces over 6-month follow-up [120]. A longitudinal multi-center study has shown that the fecal microbiota of preterm infants after supplementation with probiotic Infloran have a high relative abundance of Bifidobacterium and Lactobacillus up to 4 months of age [121]. Another multi-center cohort study showed that administering a combination probiotics mixture to preterm infants resulted in influenced the fecal microbiota profile with Lactobacillus and Bifidobacterium predominating over 5-month period [122]. In a cohort study over a 5-month follow-up, suspected bacterial signatures from Bifidobacterium and Lactobacillus were identified in the fecal microbiota of preterm infants after discontinuation of a probiotic mixture containing Bifidobacterium and Lactobacillus spp. [123].
In one cohort study, the administrated strain, B. bifidum ATCC15696 and L. acidophilus NCIMB701748, showed significant alterations in the fecal microbiota of preterm infants as demonstrated by high Lactobacillus and Bifidobacterium abundances over 1-month period [124]. A cohort study on human milk-fed preterm infants has indicated probiotic supplementation with B. longum subsp. infantis influences the fecal colonization by Bifidobacterium [125]. Probiotic supplementation with L. rhamnosus GG and B. animalis ssp. lactis BB-12 increases the relative abundance of Firmicutes and Actinobacteria and decreases the abundance of Weissella, Veillonella and Klebsiella in preterm infants during the first month of life [126]. A recent study showed that supplementation of probiotics rich in L. acidophilus and B. bifidum alters the fecal microbiota of preterm infants during the first 30 days of life by increasing Lactobacillus spp. and E. faecium abundances [127].

RCTs
A previous study resulted in increased fecal colonization with bifidobacteria and acetic acid levels in premature infants after receiving formula supplemented with prebiotic/probiotic combinations compared to those in the placebo group [128]. In a recent study, multi-strain probiotics are found to be effective in increasing fecal butyric and propionic acid levels, whereas single-strain probiotic increases fecal butyric acid levels only in preterm infants. Infants who were supplemented with probiotics showed higher fecal abundance of Bifidobacterium spp. and lower fecal abundance of Clostridium [129]. An RCT showed that preterm infants receiving probiotic supplementation with the B. breve (BBG-01) strain in conjunction with breastmilk and feeding with maternal colostrum have higher fecal Bifidobacterium abundance compared with those in placebo groups [130]. In one previous study, supplementation of a bovine milk formula with galacto and fructo-oligosaccharide mixtures has been shown to increase the relative abundance of fecal bifidobacteria in preterm infants [131]. Preterm infants supplemented with a probiotic mixture containing S. thermophilus TH-4, B. longum subsp. infantis BB-02 and B. animalis subsp. lactis BB-12 showed a significant increase in the relative abundance of Bifidobacterium spp. in the gut microbiota compared to those in the placebo group [132]. Supplementation of preterm infants with the B. lactis Bb12 probiotic strain compared with placebo modulates the gut microbiota by lowering the cell counts of clostridia and enterobacteria and increasing the cell count of bifidobacteria [133]. Probiotic supplementation with L. reuteri DSM 17938 modulates the gut microbiota composition in preterm infants by increasing the relative abundance of Lactobacillus and decreasing the abundance of Clostridium, Enterobacteriaceae and Staphylococcaceae [134]. A supplementation with a mixture of S. thermophilus TH-4, B. animalis subsp. lactis BB-12 and B. longum subsp. infantis BB-02 increases the bacterial abundance of probiotic species in the preterm infant's gut [135].

Role of Gut Microbiota and Its Metabolite SCFAs as Therapeutic Potential Agents in NEC
Gene expression including cytokines and chemokines result from histone and long non-coding RNA (lncRNA) modifications have been linked to immune cell function and inflammation in NEC [45][46][47][48][49][50][51]. Given that SCFAs have been identified as epigenetic modifier exert anti-inflammatory effects in inflammatory diseases [22,23,42], it is likely that SCFAproducing bacteria and SCFAs could perform an epigenetic role in modulating immune responses in the inflamed gut of neonatal NEC by reducing pro-inflammatory cytokines and chemokines. Thus, this section presents the therapeutic role of gut microbiota and its metabolite SCFAs in regulating NEC-related inflammation in which epigenetic changes are implicated.
Taken together, these findings suggest that SCFAs and SCFA-producing bacteria may have a potential anti-inflammatory role in neonatal NEC by protecting fetal intestinal epithelial cells against pro-inflammatory cytokines and chemokines via inhibition of different cellular signaling pathways. Figure 1 summarizes the therapeutic role of SCFAs and SCFA-producing bacteria in neonatal NEC.
Life 2023, 13, x FOR PEER REVIEW 12 of 18 (MMPI), P-c-Jun and zona pellucida protein 4 (ZP4) mRNA expression in both TLR2 and TLR4 dependent-manner [145,146]. Taken together, these findings suggest that SCFAs and SCFA-producing bacteria may have a potential anti-inflammatory role in neonatal NEC by protecting fetal intestinal epithelial cells against pro-inflammatory cytokines and chemokines via inhibition of different cellular signaling pathways. Figure 1 summarizes the therapeutic role of SCFAs and SCFA-producing bacteria in neonatal NEC.

Conclusions
SCFAs as epigenetic substrates perform a significant role in mediating microbe-host immune interactions, which could be a potential treatment for NEC-induced inflammation. During the colonization process in preterm infants, the gut is exposed to microbes that are more pathogenic but less commensal, which may contribute to NEC by increasing TLR4 signaling, leading to release of pro-inflammatory cytokines and chemokines. Breastmilk and/or formula with probiotics/prebiotics could modulate preterm infants' gut microbiota colonization by decreasing the growth of pathogenic microbes, while increasing microbial species belonging to phyla Actinobacteria (Bifidobacterium spp.), Firmicutes (Lactobacillus spp., Enterococcus spp., Streptococcus spp.) and Bacteroidetes (B. fragilis), which produce different amounts of SCFAs.
SCFAs and SCFA-producing bacteria exert anti-inflammatory effects on cytokine and chemokine production in immature enterocyte H4 cells through inhibiting different signaling pathways. Breastmilk and feeding with probiotic/prebiotic formula increase SCFA production and the abundance of SCFA-producing bacteria in preterm infants.

Conclusions
SCFAs as epigenetic substrates perform a significant role in mediating microbe-host immune interactions, which could be a potential treatment for NEC-induced inflammation. During the colonization process in preterm infants, the gut is exposed to microbes that are more pathogenic but less commensal, which may contribute to NEC by increasing TLR4 signaling, leading to release of pro-inflammatory cytokines and chemokines. Breastmilk and/or formula with probiotics/prebiotics could modulate preterm infants' gut microbiota colonization by decreasing the growth of pathogenic microbes, while increasing microbial species belonging to phyla Actinobacteria (Bifidobacterium spp.), Firmicutes (Lactobacillus spp., Enterococcus spp., Streptococcus spp.) and Bacteroidetes (B. fragilis), which produce different amounts of SCFAs.
SCFAs and SCFA-producing bacteria exert anti-inflammatory effects on cytokine and chemokine production in immature enterocyte H4 cells through inhibiting different signaling pathways. Breastmilk and feeding with probiotic/prebiotic formula increase SCFA production and the abundance of SCFA-producing bacteria in preterm infants. However, how these feeding types epigenetically determine NEC phenotype by exerting anti-inflammatory effects are still being unraveled. In conclusion, SCFAs and SCFA-producing bacteria could be potential targets in the treatment of NEC. Further studies are needed to examine whether breastmilk or feeding with probiotic/prebiotic formula could increase SCFA levels and influence the growth of SCFA-producing bacteria and the protective effects thereof on reducing NEC-related inflammatory markers through the epigenetic mechanisms. [CrossRef]